This invention relates to accoustic noise suppression apparatus and, more specifically, to accoustic noise suppression apparatus used in conjunction with a partially encased liquid-cooled power unit having a radiator type heat exchanger.
A considerable percentage of the accoustic noise generated during the operation of a power unit such as a liquid-cooled internal combustion engine is generated by the fan typically employed to drive air through a radiator for engine cooling. With present day concerns for the lowering of noise levels attendant the operation of any type of machinery as transmitted to the surrounding environment, there has been increased focus on minimizing the noise generated by fans utilized in the cooling system of power units. In many cases, fan designs have been made more efficient so as to either minimize the size of the fan required to produce a given air flow or minimize its operating speed, thereby decreasing the amount of noise generated by reason of the resulting ability to utilize smaller or slower fans. In taking such an approach a point is reached whereat only marginal improvements can be obtained since as long as a fan is required, there will be noise attendant to its operation.
To further reduce the level of noise transmitted to the surrounding environment, power units have been partially encased having openings sufficient to allow proper air flow for cooling purposes. Attempts to additionally reduce the level of noise transmitted to the environment where the power unit is partially encased have centered around the deployment of accoustic energy-absorbing material arranged in baffle type apparatus mount in front of and generally perpendicular to the existing air flow path (U.S. Pat. Nos. 3,857,453, 4,071,009, 4,122,908 and 4,121,683). However such attempts have not always been proven successful.
The present invention achieves substantial reduction of the noise associated with a power unit transmitted to the surrounding environment.